Today, in many modern manufacturing facilities, modular conveyor systems are extensively utilized to transport articles to and from various work stations during all stages of production. In recent years, manufacturers using production lines with conveyors as an integral component of the material handling system have realized reasonably significant gains in productivity and resource utilization. As a result, modular conveyor systems have become even more widely implemented and have been adapted to meet an even wider scope of the material handling needs of producers of a multitude of consumer and industrial goods. Therefore, the continual development of improved modular conveyors is necessary in order to keep pace with the demands and expectations of the users of such conveyors.
Conventional conveyor systems employing endless, modular link or roller belts or chains are typically driven at one end of an elongated guide structure, such as a rail or the like supported above the ground by a frame. The driving force is transmitted from a motive device, such as a variable speed electric motor, to a plurality of gang-driven sprockets coupled to a rotating drive structure, such as a shaft or drum. At the opposite end of the guide structure, idler sprockets are coupled to a freely-rotating idler shaft or drum. As should be appreciated, the drive and idler sprockets assist in supporting and guiding the endless belt or chain as it makes the transition from the forward run to the return run, or vice versa, at each respective end of the guide structure. Intermediate drive units, including frictional drives, may also be used in place of or in addition to the end drive unit.
Oftentimes, the belts or chains used in such conveyors are formed of a plurality of laterally repeating modular links, or unitary link sections comprising a plurality of laterally repeating link-shaped structures (collectively referred to as “links”). The links are typically formed of a low-cost high strength, wear resistant material, such as Acetal or UHMW polypropylene). To form the belt, a plurality of links or link sections are positioned in interdigitating, longitudinally repeating rows. Each row is then connected to the adjacent row by a transverse connecting rod that projects through one or more apertures in a first, usually leading portion of a first link or link section and one or more apertures or slots in a second, or trailing portion of the next-adjacent link or link section. At both lateral ends of each row, a slot is provided for receiving a locking structure, such as a tab, that holds the transverse connector rod in place. Similar types links and belts/chains formed thereof may be found in commonly assigned U.S. Pat. Nos. 4,953,693 and 5,031,757, the disclosures of which are incorporated herein by reference. Due to their low-cost, adaptability and long service life, belts formed in this fashion have gained widespread acceptance among those seeking conveying solutions.
In the past, others have recognized the potential value of a belt formed of a plurality of interconnected links, yet capable of behaving almost like it is formed of a continuous piece of material, such as a fabric. One example is found in U.S. Pat. No. 5,967,296 to Dolan, which discloses a belt including a plurality of link sections, each having laterally and longitudinally offset spherical beads with apertures for receiving a plastic transverse connector rod. Once inserted through the aligned apertures in a pair of interdigitated link sections, both ends of the connector rod are mutilated, such as by melting the ends and then smashing them against the end of the adjacent link section. The mutilated ends capture the rod in place between the link sections to form a belt section.
While the belt disclosed in the '296 patent is ostensibly capable of behaving more like a continuous piece of material than a conventional modular link conveyor belt, significant disadvantages exist with this approach. The primary disadvantage is the need for an extraordinary number of man hours to form the belt. In particular, the assembler worker must position two link sections adjacent to each other, align them in an interdigitated relationship, and then thread the narrow plastic rod through the aligned apertures. Since there are no locking tabs or the like, both ends of the connector rod must then be mutilated to ensure that it remains held in place. These actions must be repeated hundreds of times to form the belt, which greatly contributes to the manufacturing time, effort, and expense. Also, if even a single transverse rod is not correctly installed, such as if the mutilation operation is not carried out properly, it can slide out of position over time and possibly allow for a complete failure of the belt or chain. Of course, such a failure contributes to deleterious downtime, and the steps required to complete a repair operation are as time-consuming and difficult as the original assembly operation. Depending on the circumstances, the mutilated end may also inhibit one link section from freely pivoting relative to the next-adjacent link section.
In the past, others have proposed different types of conveyor chain or belts that eliminate the need for the transverse connector rod. For example, a compressible “rodless” belt in which each link includes opposed integral stub shafts that are loosely received in opposed box-shaped structures on the next-adjacent link is shown in Ashworth Brothers' U.S. Pat. No. 4,394,901 to Roinestad.
While this type of arrangement generally serves a particular need or purpose, it is not without limitations. For example, the links disclosed in the '901 patent are not readily adaptable for being scaled down to create a “micropitch” belt or chain since each includes many intricate features that would be exceptionally difficult to replicate in a substantially smaller version (e.g., a link that is less than about 6 millimeters in height). Moreover, in the case of lightweight plastic materials, the strength of structures such as the opposed integral stub shafts projecting from each link may be compromised if made substantially smaller. The height-to-pitch ratio of the belt depicted in that patent is also low (e.g., 5millimeters/27 millimeters, or around 0.25), which means that it is not well-suited for traversing over structures having a small radius of curvature, such as the rounded end of a bed in a transfer conveyor, a nose bar, or like structure.
Accordingly, a need is identified for an improved variety of modular links or link sections capable of being interconnected without the need for separate transverse connecting rods to form a relatively wide “rodless” belt. This would greatly reduce the assembly time, effort and expense without substantially compromising the durability, strength, or service life of the resulting belt or chain. In cases where the links or link sections are formed of plastic materials, the use of integral connectors formed of the same materials would also result in a weight savings per unit length as compared to the conventional modular link belt including metal (stainless steel) transverse connector rods. Forming the belt or chain from a plurality of links or link sections to create a relatively wide conveying surface, and possibly one with a completely flat top portion, would facilitate receiving and transporting many different types of articles, including possibly as part of a transfer assembly positioned between the ends of two adjacent conveyors. Driving the belt or chain could also be accomplished using a sprocket or a friction drive, which would enhance the versatility and concomitantly increase the options available to the conveyor system designer. The elimination of the connector rods would also greatly facilitate forming a “micropitch” belt or chain using such links or link sections, which could be used in regular conveyors, transfer conveyors, or the like. Overall, a “rodless” belt or chain having these capabilities would fulfill a long-felt need by solving the various problems and addressing the limitations of prior art belts or chains identified in the foregoing discussion.